In the human, the corpus luteum of pregnancy is structurally and functionally intact at the end of gestation. This proposed research is designed to determine some of the properties of the corpus leuteum of pregnancy and the puerperium. Specifically, the steroidal products of this corpus luteum will be studied to see if they are quantitatively similar to the products of the orpus luteum of the menstrual cycle, of if they are different, as is the case in the rhesus monkey. Experiments will be performed to determine whether the corpus luteum is maintained in mid-pregnancy or is rejuvenated late in pregnancy. Late rejuvenation of the corpus luteum may implicate prolactin or placental lactogen as luteotropic agents since the concentration of these hormones rises throughout pregnancy. In the monkey, suckling maintains the corpus luteum into the puerperium. Experiments will be done to determine wheter suckling prolongs pogesterone secretion in women. Our working hypothesis is that the puerperal corpus luteum is a target organ for prolactin. Utilizing radioiodinated prolactin, the binding properties of prolactin to the corpus luteum of pregnancy will be studied. BIBLIOGRAPHIC REFERENCES: Progesterone and Estrogen Secretion by Puerperal Human Ovaries. G.Weiss, I. Rifkin, Obstet. Gynecol. 46:557-559, 1975.